A need for better gene delivery has blocked the potential advancement in biomedical research and most critically development of better therapeutics that operate at the gene function level. This problem is most acute for non-dividing cells, which in fact are the predominant cell type. Thus the considerable interest in gene therapy has narrowed considerably to efforts largely developing ex-vivo approaches and use of lentiviral vectors with several important unique capabilities that include delivery to non-dividing cells. A major limitation that applies to all the lentiviral vectors developed is a lack of applicability for parenteral administration, largely due to their dependence on a finicky envelope protein that provides the critical functions of cell binding and then cell membrane fusion and intracellular delivery. Despite many efforts, including high throughput genetic engineering (e.g. "directed evolution"), the natural envelope G protein from VSV used to pseudotype retroviral vectors for many years remains one of the most effective envelope for lentiviral vectors. This problem has posed an essentially insurmountable barrier to the development of versatile targeted lentiviral vectors. Interestingly, our development of targeted nanoparticles for non-viral gene delivery has demonstrated versatile ligand-mediated tissue targeting using ligand-polymer conjugation but activity on non-dividing cells remains a major hurdle. Thus we are developing a hybrid combining our successful synthetic tissue selective targeting with lentiviral particles adept for non-dividing cells. We are developing a ligand-targeted polymer coating to replace the lentiviral envelope protein function missing in lenti-viral like particles (lenti-VLP) produced without envelope protein. Since this protein is one of the major sources of lentiviral vector instability, greatly enhanced stability is expected to be an added benefit. Our preliminary results indicate that simple homopolymer cationic polypeptides can replace lentiviral vector envelope protein function but the potency needs to be enhanced substantially. To determine feasibility of a hybrid synthetic ligand- medated targeted lenti-VLP in this Phase I research plan, we first will construct and screen a number of cationic polypeptides with defined structures to identify an SAR for binding lenti-VLP and replacing envelope protein function but without causing instability of the lenti-VLP. We then will identify methods for coupling targeting ligands to selected polypeptides without adversely affecting the cell delivery function and optimize cell selective ligand-mediated gene deliver in cell culture and for neovasculature tissue in an animal model. Public Health Relevance: A need for better gene delivery is a major barrier to development of critically needed therapeutic treatment options that operate at the gene function level. Many efforts are focused on ex-vivo uses of lentiviral vectors with many unique advantages but a major limitation is an inability for parenteral administration, due to dependence on a finicky envelope protein that provides cell binding and intracellular delivery. Conversely, our targeted nanoparticles for nucleic acids have demonstrated ligand- mediated tissue targeting but efficiency, especially for non-dividing cells remains a major hurdle. The planned study is to determine feasibility of a hybrid synthetic ligand-targeted lenti-virus like particle lacking envelope protein and optimization of cell selective ligand-mediated gene delivery for neovasculature tissue in an animal model.